It's all planned in 3 parts. That changes everything. Because for part three, most of stories claim for and ending or some kind of change.

You were talking about Spider-man 3. To me, Venom or not, the problem was that they had to do something more extreme but at the same time they had to be thinking in leaving stuff for the fourth movie. That's how there's a convulted Peter-Mary Jane arc there, but in the end they end up without much change.

Definitely. I'm not even the biggest Spidey 3 hater in the world, though it's frustrating in that it was a missed opportunity in many ways. But yeah, it felt like a half-assed conclusion that had the scale you'd expect from an ending, but that's about it. Besides Harry's character arch, it didn't really wrap anything up. The theme of the film, forgiveness, was not a bad one to have but it felt like Peter's "lesson of the day", not something that unified all three movies.

So in short, you're absolutely right that you can't do a third/ending movie justice if there are plans in place to make more movies.